This disclosure relates to an improvement in moisture sensitive layers and in particular to polyvinyl butyral (PVB) film or sheet products and more particularly to an improvement in the thermochromic PVB products described in the following commonly owned U.S. patents and applications: U.S. Pat. No. 7,538,931; U.S. Patent Publication No. 2008/0105851; U.S. Pat. No. 7,525,717; and U.S. Pat. No. 7,542,196, all to Byker et al. and all of which are incorporated herein by reference. As described in the '717 patent, thermochromic PVB products have a thermochromic layer that includes a polymer, at least one transition metal ion, at least one high epsilon ligand capable offorming a high epsilon metal-ligand complex with the transition metal ion and at least one low epsilon ligand capable of forming an low epsilon metal-ligand complex with the transition metal ion. PVB is a copolymer sometimes designated as poly(vinyl butyral-co-vinyl alcohol-co-vinyl acetate). PVB is widely used in making safety glass laminates for motor vehicle windshields and architectural safety glass.
Various film and layers including PVB films have a strong propensity to absorb water. It is a common practice when manufacturing these films or sheets to maintain low relative humidity in the manufacturing environment and carefully package the rolls of film or sheet in moisture resistant packaging. Some of the thermochromic PVB films or sheets disclosed by Byker et al. are even more hygroscopic and more sensitive to absorbed moisture and hence it is not uncommon to store rolls of thermochromic PVB films or sheets under vacuum in the presence of desiccant. Moisture in the PVB films or sheets disclosed by Byker et al. is undesirable because it can decrease the performance of the thermochromic system in the films and the moisture can lead to deleterious reactions that decrease durability of the films.